From this little rock that we are based, we have a grandstand view to explore our galaxy and the galactic neighborhood. The Sun, our closest star, 150 million kilometres away, is all we are able to see when it is out, but every night when this sun disappears from our sight, thousand more fill up the night sky. The most privileged places on our planet are able to observe up too 10,00 stars with just the naked eye. All of these stars are part of the galaxy we call home.
What is the Galaxy?
A galaxy is a large collection of stars, gas and dust all bound together by gravity. It is a place where stars live and die, where the life cycles of our universe are played out on a gargantuan scale. We think there are about 100 billion galaxies in the observational universe each containing many millions of stars.
Smaller and larger galaxies
Dwarf galaxies have as little as ten million stars. Where as the largest galaxies, the giants have been estimated to contain 100 trillion stars. It is now well accepted that these galaxies contain much more than just the matter our telescopes can pick up. A new form of matter is believed to occur unlike anything we have discovered on earth, giant halos of dark matter, which only interacts weakly with normal matter.
Despite this, the gravitational effect of dark matter dominates the galaxies today and probably dominated the formation of the galaxies in the early universe. This is believed, because we now think that 95 per cent of the mass of our galaxies is made up of dark matter, including that of our own, the Milky Way. Which makes you think that maybe luminous stars, planets, gas and dust are just more of an after thought. Although saying this, it is highly unlikely that dark matter can form into complex and beautiful structures like stars, planets and people, one might claim therefore it is far less interesting. One of the twenty first century’s greatest challenges within physics is this search for the nature of dark matter.
Where did the name come from?
The word ‘galaxy’ originates from the Greek word galaxies, meaning milky circle. First it was used to describe the galaxy that dominates our night skies, even though at the time, the Greeks could have had no real concept of its true size.
Views of our galaxy
One of nature’s greatest displays is being able to watch the core of our galaxy rise in the night sky, although has been robbed from us by our cities light, taking away this majestic nightly display. For many it appears like storm clouds rising on the horizon, but as the Earth turns nightly towards the centre of our galaxy, the hazy band of light reveals itself to be clouds of stars. Greek myths describe this happening to be spilt milk from the breasts of Zeus’s wife, Hera, creating a faint band across the night sky. This tale is the origin of the most recent name for our galaxy – The Milky Way.